Heating of tissue to temperatures which cause cell death can be used as a form of cancer treatment. Heating to moderately increased temperatures (on the order of 42 to 45 C.), known as hyperthermia, has been used, for example, to damage or kill cancer cells and to make cancer cells more sensitive to collateral modes of treatment. Increasing the temperature to at least 50 C. for extended exposure (minutes) causes coagulation necrosis, a method known as ablation. Different forms of energy can be used to induce cell death, including microwaves, radio waves, and ultrasound.
In treating tumors or other cancers, an optimum effect can be achieved if the tumor is locally heated such that healthy tissue remains unaffected. The treatment can be effected through external approaches, such as that undertaken for treating skin cancer. An external approach to treating skin cancer, for example, utilizes microwaves with slight tissue penetration depth to induce cell death in melanoma tumors.
For treating deeper lying tumors, heat sources can be inserted directly into a tumor to induce cell death or cause ablation. A procedure known as radio frequency ablation (RFA) utilizes radio frequency radiation, which is applied to the tumor. Radio frequency also has been used to treat deeper lying tumors and cancerous tissues, but typically only for regional hyperthermia. According to this technique, large volumes of tissue are usually heated by placing external applications around that portion of a patient's body that is to be treated.
Conventionally, if local heating of a tumor or part of a tumor is to be undertaken, short-wavelength radiation can be used, the tissue penetration depth being relatively slight. An antenna can be used to transfer the energy from the source to the tumor. Because of the small penetration depth, this technique can be effective for skin cancers, but typically cannot be used to effectively treat deeper lying tissue. Alternatively, for deeper penetration, an interstitial technique can be used, according to which a probe is inserted into the tumor in order to induce cell death by transfer of energy from the tip of the probe to the tumor.